The use of ketene dimer based agents in the paper industry to impart sizing, or water resistivity, to paper products is well known. Such agents are commercially available from Hercules Inc. Wilmington, Del. under trade names such as AQUAPEL.RTM. and HERCON.RTM.. Patents disclosing the compositions, variations and uses of these types of agents are:
Inventor Patent No. Issued Aldrich et al. 3,922,243 Nov. 25, 1975. Anderson 3,957,574 May 18, 1976. Aldrich, et al. 3,990,939 Nov. 9, 1976. Aldrich 4,017,431 Apr. 12, 1977. Aldrich et al. 4,087,395 May 2, 1978. Dumas 4,240,935 Dec. 23, 1980. Dumas 4,243,481 Jan. 6, 1981. Dumas 4,279,794 Jul. 21, 1981. Dumas 4,295,931 Oct. 20, 1981. Bankert et al. 4,407,994 Oct. 4, 1983. Bankert et al. 4,478,682 Oct. 23, 1984. Edwards et al. 4,861,376 Aug. 29, 1989. Cenisio et al. 4,919,724 Apr. 24, 1990. Walkden 4,927,496 May 22, 1990. Nolan et al. 5,484,952 Jan. 16, 1996. Zhang 5,525,738 Jun. 11, 1996.
The disclosures of which are incorporated herein by reference.
These sizing agents when added to the wet end of the paper machine, at the size press, or to the finished product in an off-machine application impart water resistivity to the paper, by decreasing the hydrophilicity of the sheet. The use of these sizing agents in writing paper, liner board, grocery bag and milk carton is well known, as all of these paper products require sizing.
These types of sizing agents are known to produce very hard sized (high resistivity to wetting) material such a milk carton. The use of these sizing agents in tissue and towel, although not unknown, has been very limited, because water resistivity is not desirable in these products. To the contrary, it has generally long been a goal in the tissue and towel industry to increase rather than decrease the rate at which the product is wetted and the total amount of water that the product can absorb. An example, however, of the use of ketene dimer sizing agents in tissue and towel products to increase water resistivity is found in European Patent Application No. 0 144 658 in the name of Dan Endres, assigned to Kimberly-Clark Corp.
It has been discovered that the use of deactivated ketene dimer sizing agents in tissue and towel increases the softness to these products while not materially effecting their water absorbtivity or hydrophilicity.